Vehicles today commonly come equipped with speech interfaces for the driver or other user. These speech interfaces can be used by automatic speech recognition (ASR) systems and/or by an onboard telematics unit to permit the user to carry on voice telephone calls. In some vehicles, both the ASR and telephony capabilities are integrated together into a single telematics unit having the speech interface. Telematics units that utilize these speech interfaces are commonly now offered as original equipment on many vehicles and in many cases come as standard equipment. OEM installation of such systems permits the manufacturer to integrate the telematics unit and its speech interface in with other vehicle systems. For example, the audio entertainment systems installed on these vehicles by the manufacturer can include traditional stereo components, satellite radio, as well as integration in with an on-board video entertainment. Operation of the telematics unit can be coordinated with the vehicle audio system so that, for example, the speech from the telematics unit's speech interface is played through one or more of the audio system speakers at a volume controllable by the radio volume knob. Then, when a call comes in to the telematics unit or when the user initiates a speech recognition session with the telematics unit, the radio can be automatically muted while the call or session is in effect and the volume of the caller or ASR system speech can be adjusted by the user via the radio's volume knob. As used herein, these telephone calls and speech recognition sessions are referred to generically as speech sessions.
In one known system that integrates the telematics unit audio output with the vehicle's audio system, each time a speech session is begun, the audio system volume is set back to its previous setting that existed at the end of the most recent speech session. Thus, if the user had finished his or her previous session with the volume set at one-third of maximum volume, then at the initiation of the next speech session, then regardless of the current audio system volume set by the user for music or other infotainment, the volume is automatically adjusted to that one-third setting. The exception to this approach is that the audio system is configured with a minimum volume setting, so that if the user had ended the last speech session with the volume turned all the way down, the new session will begin with the volume at some predetermined minimum volume above zero. In this way, the user will be certain to hear the ASR system or caller.